The present invention relates to a method of making an antenna, and in particular to a method of making a dual band microstrip antenna.
Referring to FIG. 1, a conventional microstrip antenna comprises an insulative substrate 20xe2x80x2, a conductive patch 21xe2x80x2 attached to one surface of the substrate and a ground plane layer 22xe2x80x2 attached to another, opposite surface of the substrate. RF signals are fed to the antenna by a coaxial cable or a conductive strip 23xe2x80x2. Electrical and magnetic fields are formed between the patch and the ground plane layer and electromagnetic wave radiate from gaps between and around the patch and the ground plane layer.
Parameters of the elements of the microstrip antenna will affect operating performance of the microstrip antenna. To achieve desirable performance through selecting, calculating and testing parameters of the elements, a method for making a microstrip antenna generally comprises the following steps:
1. selecting the thickness t and the relative dielectric constant xcex5r of the insulative substrate;
2. selecting the width W of the conductive patch 21xe2x80x2 using the equation
W=(xcex/2)[2/(xcex5r+1)]1/2 
where xcex=c/f, and where xcex and f are respectively the wavelength and frequency of the operating signals, and c is the speed of light in a vacuum;
3. calculating the effective length L and the effective dielectric constant xcexe of the conductive patch 21xe2x80x2 using the equation
xe2x80x83L=xcex/2xcex5e1/2xe2x88x922xcex94L, where
xcex94L=(0.412t)(xcex5e+0.3)(W/t+0.264)/(xcex5exe2x88x920.258)(W/t+0.8) and 
xcex5e=(xcex5r+1)/2+[(xcex5rxe2x88x921)/2](1+12t/W)xe2x88x921/2, where 
xe2x80x83xcex94L is the effective extending length of the conductive patch;
4. selecting a feed point location on the patch;
5. measuring the radiation pattern and Voltage Standing Wave Ratios (VSWR) of the microstrip antenna; and
6. if the measured results do not satisfy operating requirement, returning to the first step and repeating all steps until a satisfactory result is achieved.
A conventional dual band microstrip antenna is disclosed in U.S. Pat. No. 5,561,435. Referring to FIG. 2, the dual band microstrip antenna comprises a first, second and third superimposed dielectric layers 4xe2x80x2, 6xe2x80x2, 16xe2x80x2, a ground plane 2xe2x80x2 on one external surface, a conductive patch 18xe2x80x2 on an opposite external surface, and parallel conductive strips 12xe2x80x2, 14xe2x80x2 at the interface of the dielectric layers 6xe2x80x2, 16xe2x80x2, closer to the patch 18xe2x80x2 than to the ground plane 2xe2x80x2. The dielectric constant of the second layer 6xe2x80x2 is different from that of the first and third layers 4xe2x80x2, 16xe2x80x2. As disclosed above, the performance of the dual band microstrip antenna can be optimized by adjusting the thickness and the dielectric constants of the dielectric layers 4xe2x80x2, 6xe2x80x2, 16xe2x80x2.
However, the dielectric constant is related to the material of the layer, so adjusting the dielectric constant implies changing the material of the layer and it is difficult to get an exact value of dielectric constant in this way. Furthermore, a minimum value of the dielectric constant is close to but is no less than 1 (as is air), and the thickness t of the dielectric layer generally should be far less than xcex for considerations of size, so adjusting the performance of the microstrip antenna by varying thickness and dielectric constant is realistically very limited. Each value of thickness and dielectric constant of each of the dielectric layers 4xe2x80x2, 6xe2x80x2, 16xe2x80x2 will affect the whole performance of the antenna in two operating frequency bands at the same time.
Hence, an improved method of making a dual band microstrip antenna is desired to overcome the above-mentioned shortcomings of the existing method.
A primary object, therefore, of the present invention is to provide an improved method of making a dual band microstrip antenna which allows adjusting the performance of the antenna individually and conveniently in each operating frequency band.
Another object is to provide a method of making a dual band microstrip antenna, which allows adjusting the performance of the antenna in a wider range.
A dual band microstrip antenna made by a method in accordance with the present invention comprises a dielectric substrate, a ground plane layer attached to a bottom surface of the substrate, a first and second conductive patches separately elevated above and parallel to a top surface of the substrate, a first and second conductive posts respectively elevating the first and second radiating patches above the substrate and electrically connecting the first and second patches with the ground plane layer, and a first and second coaxial feeder cables. The method for making the dual band microstrip antenna comprises adjusting the height of the first and second conductive posts to achieve a good performance of the dual band microstrip antenna.
Other objects, advantages and novel features of the invention will become more apparent from the following detailed description of a preferred embodiment when taken in conjunction with the accompanying drawings. The copending application with the same applicant and the same assignee as the invention, titled xe2x80x9cDUAL BEND MICROSTRIP ANTENNAxe2x80x9d filed on the same date with the invention is referenced hereto.